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Old 26-09-2020, 03:43 PM
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leon
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Is this wire to thin to run an electrical current please

Hi Guys, to any members experienced in electrical contraptions, please

I need to power a camera battery adapter which needs 7.5 volts and 2.0 amps to work effectively.

So what is the minimum wire that i can use to do this.

I went to Bunnings to buy some two ply to do this job but came home with heavy duty speaker wire instead by mistake so now i have 30 meters of this wire, I don't think Bunnings will exchange this purchase

Would this wire be OK to run this adapter, it is 0.75mm in diameter

I thought I had better ask before I blow up something

Thank You in advance
Leon
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Old 26-09-2020, 04:02 PM
DarkArts
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That depends, but it sounds too small for the application. You may have 30m of wire but how long does the run need to be? Also, what is the voltage drop tolerance (or what is the voltage of the source and minimum voltage requirements of camera/battery adapter)?

You can play with the numbers yourself using this calculator to see what gauge you need for any arbitrary cable length. For example, if a 5% voltage drop was tolerable from a 7.5V source, then at 2A, you would need 10mm2 (gauge 8 AWG).

Here's another useful voltage drop calculator.

If you really need a long run, you might consider running AC closer to the camera and using a shorter DC run.
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Old 26-09-2020, 07:10 PM
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billdan (Bill)
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Hi Leon,

I also think the wire you purchased is too thin, at 0.75mm diam, that has a cross sectional area of pi(r≤) = 3.141 x .375≤ .

Or approx 0.44 square mm, according to the attached PDF table that area will not support 2 Amps and only 1 amp up to 5 metres in length.

This table suggests you need an area of 1.84 square mm to carry 2 amps up to 15 metres, thicker wire if you want to go longer. Now 1.84 square mm is about 1.5mm in diameter ( Diam = 2 (sq root Area/pi.).

P.S. If you haven't used the cable, Bunnings should exchange it or give you a refund.
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Old 27-09-2020, 05:43 AM
astro744
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Why not get a 30m extension lead and place the camera adapter at the destination and not the source. Youíll get a little voltage drop on the AC but most adapters will accept 100-230V. Running the DC that far will require much larger cable. Note cable is typically always referenced as Cross Sectional Area.

Bunnings list the speaker wire as 0.75mm but they also say list 24/0.2 stranded. This means 24 conductors in a bundle at 0.2mm diameter each.

CSA = (0.2/2)^2*3.141*24 = 0.754mm2

I believe the Bunnings listing should state 0.75mm2.

In any case if you are running the DC over a long length you do need to consider voltage drop and the 0.75mm2 is well under sized.

If you are running the AC over the 30m then you must use a cable with insulation suitably rated for the voltage, I.e. 230V as the circuit no longer qualifies as extra low voltage. (Such power cables will typically have a 450V rating or often 0.6/1kV). Note if your extra low voltage cables is run adjacent any power cable then the ELV cable insulation must also be the same rating as the power cable. You must also consider earthing. Either get an extension lead or qualified electrician to run a dedicated circuit.

The insulation of the speaker wire would be extra low voltage at best. I looked on the Olex site for the product and was surprised to see no voltage rating for the product. Resistance is listed for voltage drop calcs. It is an audio cable and Iím not sure of their max voltage rating requirements.
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Old 27-09-2020, 07:31 AM
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Wow, that calculator is seriously conservative (As is the PDF) The calculator suggests 16# wire for 2A at 5M for 5% drop, that suggests 1.2 ohms in 10M of wire, 0.12 ohms per meter! (10M not 5M as assuming I understand that calculator correctly that is ROUTE length, so includes both conductors of a circuit out and back)

I know I am using good wire in my race car but for the Tefzel coated, tin plated copper stuff I am using there even 24# wire is around a half of that resistance at 0.071 ohms per meter, 16# is 0.014 ohms per meter. The heaviest draw circuits in my race car have 2 X 16# wire (Fuel pumps which can draw 15A continuously) and people reckon I have wasted weight and money going too big.

That said, there is no real penalty for going a bit big in your application Leon. Just you don't need to go too silly with it. A bit of GOOD quality 16# will probably do you well. Depending on the length you need to run (Like was written above this assumes ELV that you can legally fiddle with yourself) you could probably get a length of two core DC from Repco. I have used some of that stuff in my scope gear rather than the Tefzel stuff I use in my race car which is a lot more expensive.

Last edited by The_bluester; 27-09-2020 at 08:25 AM.
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Old 27-09-2020, 07:35 AM
Wilso (Darren)
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Hi Leon,
I normally go to Jaycar to get my electrical gear. They sell many different size cables by the metre and are very helpful to answer any of your questions. Good luck
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Old 27-09-2020, 03:11 PM
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Thank you all for your responses, lots of good info here.

Yes to answer a question, I do need a long run, but was hoping to get away from a heavy extension lead, hence the two ply stuff.
I am going to Bunnings tomorrow and see if they will actually exchange this purchase for some heavier cable.

Leon
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Old 27-09-2020, 07:02 PM
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https://community.dur.ac.uk/p.m.john..._thickness.htm
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